Battery sensing method and apparatus

ABSTRACT

A method and apparatus is provided the battery sensor for a large-scale battery system. More specifically, the present disclosure relates to the architecture and measurement scheme for a high-accuracy battery voltage sensor based on a calibration scheme. The present disclosure also related to the architecture and measurement method for a cell-level current sensor to effectively and reliably manage a battery pack.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application of InternationalPatent Application No. PCT/US2015/031953, filed on May 21, 2015 whichclaims the benefit of U.S. Patent Provisional No. 62/001,746, filed on,May 22, 2014, the contents of which are incorporated herein by referencein their entireties.

BACKGROUND OF THE INVENTION

Statement of the Technical Field

The inventive arrangements relate to battery sensors for large-scalebattery systems, and more particularly to systems capable of measuringelectrical characteristics of large-scale battery systems down to thelevel of individual cells.

Description of the Related Art

Large scale battery systems are becoming increasingly important incertain applications. For example, such systems are commonly used inhybrid/electric vehicles (xEV) and other types of energy storage systems(ESS). A battery pack used in these applications may have a single pairof output terminals, but internally the pack is commonly comprised ofmany individual battery cells working together. The number of batterycells and the configuration of cell connection are selected to meet therequirements of a particular battery pack with regard to output voltageand power capacity. The number of cells connected in series determinesan output voltage for the battery pack. The number of cells connected inparallel determines the amount of current flow and power capacity of thebattery pack.

Proper electric and thermal management of large-scale battery systems(i.e., battery packs) is imperative. Such management is particularlyimportant in systems that consist of many individual battery cells asmay be used in hybrid/electric vehicles or energy storage systems.During operation, voltage, current, and temperature differences in theindividual battery cells can lead to electrical imbalances from cell tocell. These imbalances are known to decrease pack performance and lifetime and are therefore to be avoided whenever possible.

SUMMARY OF THE INVENTION

Embodiments of the invention concern a sensing system for a battery packwhich includes a plurality of battery cells. The sensing system includesa plurality of single battery cell sensor modules (SCSMs), each for oneof the plurality of battery cells in the battery pack. Each SCSMincludes an analog switching multiplex, an analog-to-digital converter(ADC), and a signal conditioner. The signal conditioner conditionssignals received at the analog switching multiplex and communicates theconditioned signals to the ADC. Also included in each SCSM is areference voltage generator which generates a plurality of referencevoltages which define the scale of the ADC and a calibration engine. Theanalog switching multiplex is responsive to a control system to selectwhen in a sensing mode one or more of the plurality of battery sensorsignal inputs based on a predetermined operation schedule.

The calibration engine provided in each SCSM is configured to determinea drift error associated with the plurality of reference voltages andcorrect the drift error at the reference voltage generator. In thisregard, the reference voltage generator generates top and bottomreference voltages which define the full-scale input range for the ADC.The top and bottom reference voltages are applied to inputs of thesignal conditioner when the SCSM is in a calibration mode to generate anoutput calibration voltage. The calibration engine is configured todetermine the drift error value by calculating a difference between apredetermined reference value and a measured value output of the ADC inthe calibration mode. According to one aspect, the signal conditionerincludes a voltage divider and the calibration engine is configured toautomatically use the drift error value to adjust the voltage divider.Further, the calibration engine is configured to automatically adjustthe top reference voltage and the bottom reference voltage based on thedrift error value which has been determined. The top reference voltageand bottom reference voltage can be adjusted using two separatedigital-to-analog converter channels.

The battery sensor signal inputs can include a voltage sense signal, acurrent sense signal, and a temperature input signal. According to afurther aspect, each SCSM can be configured to use one or more of thebattery sensor input signals to determine a voltage potential across ashunt resistance. The shunt resistance is advantageously an inherentresistance of a portion of a conductive positive or negative outputterminal of a single battery cell of the plurality of battery cells. Inthis regard, the signal conditioner can include two voltage conditionerswhich respectively independently condition an input voltage potential ateach of two distinct points on one of the positive output terminal orthe negative output terminal of each battery cell.

The system can also include a master controller which receives from eachof the single battery cell sensor modules a value which specifies thevoltage potential across the shunt resistance for each of the batterycells. The master controller is configured to calculate the shuntresistance value for each single battery cell using the value whichspecifies the voltage potential across the shunt resistance for eachbattery cell and based on a total battery pack current. The mastercontroller is further configured to periodically determine an individualbattery cell current for each individual battery cell after the shuntresistance value of each single battery cell has been determined. Itdoes so by using the shunt resistance value stored for each batterycell, and a periodically measured shunt voltage for each battery cell asmeasured at each of the single battery cell sensor modules. Accordingly,the master controller can automatically determine a condition of eachbattery cell based on the battery cell current for each battery.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described with reference to the following drawingfigures, in which like numerals represent like items throughout thefigures, and in which:

FIG. 1 is a block diagram of a large-scale battery system.

FIGS. 2A-B are commonly used battery sensing architectures.

FIG. 3 is a battery pack sensing architecture that is useful forunderstanding the invention.

FIG. 4 is a single cell sensor architecture that is useful forunderstanding the invention.

FIG. 5 is a timing diagram for sensor calibration and sensingoperations.

FIG. 6A shows additional details of a single cell sensing architectureof FIG. 4.

FIG. 6B is a diagram which is useful for understanding a voltagecalibration scheme.

FIG. 7 is a block diagram of a cell-level current sensor architecturethat is useful for understanding the invention.

FIG. 8 is a block diagram of a battery cell current measurement blockthat is useful for understanding the invention.

DETAILED DESCRIPTION

The invention is described with reference to the attached figures. Thefigures are not drawn to scale and they are provided merely toillustrate the instant invention. Several aspects of the invention aredescribed below with reference to example applications for illustration.It should be understood that numerous specific details, relationships,and methods are set forth to provide a full understanding of theinvention. One having ordinary skill in the relevant art, however, willreadily appreciate that the invention can be practiced without one ormore of the specific details or with other methods. In other instances,well-known structures or operation are not shown in detail to avoidobscuring the invention. The invention is not limited by the illustratedordering of acts or events, as some acts may occur in different ordersand/or concurrently with other acts or events. Furthermore, not allillustrated acts or events are required to implement a methodology inaccordance with the invention.

The present disclosure relates to the architecture and measurementscheme for a high-accuracy battery voltage sensor based on a calibrationscheme. It also concerns an architecture and measurement method for acell-level current sensor to effectively and reliably manage a batterypack. Moreover, it is related to an architecture and measurement methodfor a battery sensor to reliably and effectively manage a multi-cellbattery module.

According to one aspect, the inventive arrangements concern asingle-cell battery sensor. The sensor combines a high-accuracy voltagesensor with a cell-level current sensor, especially suitable forlarge-scale battery systems. The high-accuracy voltage sensor deploys acalibration technique to compensate a reference voltage drift and devicemismatch. Combined with an n-bit ADC, the voltage sensor can achievehigh accuracy with wide measurement range. The cell-level current sensorfeatures a shunt-type current measurement technique with low offsetdrift. The cell-level current sensor can obtain reasonable linearity forhigh-level pack current. The invented voltage and current sensors aredirectly mounted on a battery cell to improve measurement accuracy, toreduce the measurement failure probability, and to easily diagnosebattery conditions. The single-cell battery sensor is proposed to beused in a multi-cell battery sensor. A multi-cell battery sensor iscomposed of multiple single-cell voltage sensors and isolated powertransfer units, and a unique switching scheme for efficient isolatedpower transfer technique.

Illustrated in FIG. 1 is a general configuration of a large-scalebattery system 100. The number of necessary cells and the configurationof cell connection are selected to meet the requirements of a particularbattery pack with regard to output voltage and power capacity. While thenumber of cells connected in series determines battery system's outputvoltage, the number of cells connected in parallel determines the amountof current flow and power capacity. Cells 102 are usually connected inparallel first to form a battery module 104 and then connected in seriesto form the pack 106, as shown in FIG. 1. For convenience the cells 102in FIG. 1 are shown as being arranged in rows and columns. A batterypack arranged to have P cells in a row and S cells in a column, contains(P*S) cells. The cells in a row (Cell_(s,p|p=1 . . . P)) that form amodule 104 will each have a same voltage of V_(s), while the sum of cellvoltages in a column is equal to a pack voltage; Σ_(s=1)^(S)V_(S)=V_(PACK). The cells in a row (Cell_(s,p|p=1 . . . P)) may havedifferent cell current of I_(CELL) ^(s,p), and the sum of cell currentsin a row is equal to the pack current; Σ_(p=1) ^(P)I_(CELL)^(p)=I_(PACK).

During the operations of a battery system, voltage, current, andtemperature differences among battery cells can lead to electricalimbalances from cell to cell, and reduce the performance and life timeof the battery. Cell voltage measurement is straightforward, and itsaccuracy directly relies on the resolution of an analog-to-digitalconverter (ADC) that is used for effecting such measurement. Referringnow to FIG. 2A, there is shown a block diagram of modular-type sensingarchitecture 200. Sensing modules (SMs) 210 measure the voltages atvarious taps in series-connected battery cells 202, and calculate eachcell voltage as the voltage difference between two taps. A controlmodule 212 is provided for controlling the operations of the sensingmodules. Alternatively, a distribution-type sensing architecture 220 canbe used, as shown in FIG. 2B. In a distribution-type sensingarchitecture, a plurality of sensing modules 230 can directly measurethe voltage across each battery cell 222. The sensing modules can becontrolled by a control module 230. The cell sensing modules 210 arepowered by the respective battery cell 22 being measured. Themeasurement error in each case mainly depends on the drift of thereference voltages used for the ADC in the sensing module, process andtemperature variations, which affect the ADC performance, and/or agingeffects. In FIGS. 2A and 2B, the connection between sensing modules anda control module can be wired communications such as serial peripheralinterface (SPI), RS232, controller area network (CAN), or wirelesscommunications.

A battery sensing architecture is shown in FIG. 3 for use in the contextof a large-scale battery system 300. The battery sensor architectureincludes current and voltage sensing at each battery cell. Such anarrangement facilitates measurements of current and voltagecharacteristics at the level of individual battery cells 302 and offersimprovements over conventional battery monitoring systems.

As shown in FIG. 3, battery cells 302 are connected in parallel to formbattery modules 304. For convenience in understanding the invention,these parallel connected battery cells comprising each module areillustrated to be disposed in a row. The battery modules are thenconnected in series to form the battery pack 306. As an aid tounderstanding the invention, the battery cells comprising each moduleare shown as being aligned in columns with battery cells of adjacentmodules. According to one aspect of the inventive arrangements, acell-level voltage and current sensor is integrated into a sensorintegrated circuit (IC). Each sensor IC is integrated into a circuitboard to form a single cell sensing module (SCSM). One such sensingmodule is then directly mounted at or on each individual battery cell302.

FIG. 3 illustrates a voltage and current sensor implementation on anS-series, P-parallel battery pack, which corresponds to a battery sizeof S*P. The P parallel-connected cells can facilitate measurement ofeach cell's voltage and individual cell current at the same time.Theoretically, all the battery cells in a row associated with a module304 should have the same voltage since they are connected in parallel.In actual practice, the voltages measured by each SCSM will vary to someextent due to quantitative variation or dispersion. These variations aremainly due to reference voltage drift or ADC's performance deviation.Therefore, a host controller or master module 310 will be able tocalculate a more accurate voltage V_(s) for the cells 302 comprising aparticular module 304 if the value is obtained by applying a statisticalfunction or estimation based on the plurality of measured voltagesobtained for the battery cells in a row. The application of suchstatistical function or estimation method can help remove voltagemeasurement errors.

Theoretically the pack current (I_(PACK)) show in FIG. 3 is evenlydivided into each of the separate battery cells in a row. Thisassumption is usually reasonably accurate when the battery pack is firstassembled, but over time there can be more current in one cell thanothers. Such unbalanced cell current flow sometimes represents cellperformance degradation or hidden trouble spots due to aging or defects.Therefore, it is important to measure the current flowing through eachof the individual battery cells 302 in a battery pack 306. Suchinformation can advantageously provide the triggering means foridentifying when an aging or defective battery cell should be replaced.

Referring now to FIG. 4, there is shown an exemplary SCSM 400 that issuitable for a distribution-type sensing architecture 220, as shown inFIG. 2B. The input stage of the SCSM has multiple input terminals suchas BAT_V, BAT_T, and BAT_I corresponding to certain battery parameterswhich are used to estimate the condition and status of a battery cell.For example, the measured battery parameters can include batteryterminal voltage (BAT_V), battery body temperature (BAT_T), and/orcell-level battery current (BAT_I). Each of these terminals can beelectrically accessed or selected by means of a switch 402. The SCSM 400can also include a signal conditioner 404, a single-to-differential(S2D) converter 408, an n-bit ADC 410 and a calibration engine 412.

A signal conditioner 404 as used in the SCSM is one of the criticalcomponents of measurement and calibration. Its pivotal roles are toalign the level of cell input voltage to a full-scale range of the ADC,as well as to detect the mismatch of the ADC reference voltage. It canbe, for example, a voltage divider that is a series connection of twopassive devices to achieve high linearity. The S2D converter is used toreduce the negative effects associated with common mode noise, which canlead to measurement errors. Notably, the calibration engine isadvantageously embedded in the SCSM 400 to also minimize measurementerrors.

The SCSM 400 is directly powered by a battery cell on which it ismounted. As such, the SCSM uses a voltage regulator 414 such thatregulated power is supplied to the ADC in order to enhance power supplyrejection ratio (PSRR). A control unit 406 can be provided to controlcertain operations of the SCSM. The control unit can be amicrocontroller, an application specific integrated circuit, or anyother type of dedicated hardware component suitable for implementing thecontrol and/or scheduling functions described herein. A data transceiver407 can also be provided in the SCSM to facilitate communicationsbetween the SCSM and a control module 310. The data transceiver can bedesigned to facilitate wired communications such as serial peripheralinterface (SPI), RS232, controller area network (CAN), or wirelesscommunication.

An SCSM 400 as described herein can have four predefined operationmodes. The operation modes include (1) power-down, (2) calibration, (3)standby, and (4) active mode. The selection and operation of one or moreof these modes can be under the supervision of the control unit 407. Inpower-down mode, all the functional blocks in the SCSM 400 are turneddown to minimize the current draw. The calibration mode (sometimesreferred to herein as the built-in self-calibration or BISC mode) isnecessary to correct the errors or drifts of reference voltages due toprocess or temperature variations.

As shown in FIG. 5, the BISC mode is initially activated just afterpower-up transition 502. Further BISC mode activation can occur based ona predetermined schedule or predetermined conditions. An EN_BISC signalcontrols the sequence of the calibration process. After calibrationmode, the SCSM 400 can enter a standby mode at 504, but at some pointthe sensor enters the active mode at 506 by enabling EN_READ=“ON” andstarts to measure battery cell conditions. After a power control (PC)period, a single-cell battery sensor selects (e.g. sequentially selects)one of multiple sensor input terminal such as BAT_V, BAT_T, and BAT_I.Or, it can measure only one single input terminal signal, if necessary.Except during active mode or calibration mode, the SCSM stays in standbymode to minimize power consumption. During standby mode, only a part ofpower management unit (PMU) and a watchdog timer are powered up so as tominimize electric current draw. The various control signals describedherein can be generated by control unit 407.

Referring now to FIG. 6A, there is shown a second block diagram of SCSM400 which includes additional components associated with theself-calibration feature. These additional components include an exampledesign of a signal conditioner 404, a reference voltage generator(RefGen) 602, and a data register 606. Also shown in FIG. 6A are certaindetails of the calibration engine 412, including m-bit subtractor 616,m-bit digital-to-analog converters (DACs) 618 a, 618 b, and upper/lowerDAC controllers 617 a, 617 b.

The reference voltage generator 602 provides two reference voltages froma stable source, such as a bandgap voltage reference generator. Thesetwo reference voltages include a top and bottom reference voltage, whichare respectively designated as VR_T and VR_B in FIGS. 4 and 6A. As isknown, a bandgap reference generates a constant voltage irrespective ofpower supply variations, temperature changes and the loading on thedevice. However, since only the linear terms of current are compensatedat bandgap reference, the higher-order terms will limiting thetemperature drift of the device to around 20-50 ppm/° C. over atemperature range of 100° C. Besides temperature drift, initial accuracyand drift due to aging must always be trimmed over the operatingtemperature range and expected lifetime of the device.

The built-in self-calibration consists of two functions, detection andcorrection. The detection function is performed by measuring the outputvoltage of a voltage divider 600 while the voltage divider is connectedwith reference voltages, VR_T and VR_B. The output of the voltagedivider is converted to digital data and compared with an idealreference voltage value 620 in the digital domain. The discrepancybetween the measured code and the ideal code in each case is stored atan m-bit calibration register within the calibration engine 412. Thelength of the calibration register can be determined by the anticipatedmagnitude of any mismatches. The most significant bit (MSB) of thecalibration register can be used to represent the sign of mismatch,either over or under the ideal reference voltage. Accordingly themagnitude of the drift voltage can be represented by a digital data wordcomprised of m−1 bits.

The DACs 618 a, 618 b together comprise a dual-channel calibration DAC(CalDAC). Each DAC 618 a, 618 b is an m−1 bit DAC with an n-bitresolution. The MSB determines which DAC will be used for calibration,the m−1 bits determine the amount or magnitude of the error to becorrected. The correction process measures relative cell voltage withrespect to the reference voltages. Therefore, the absolute accuracy ofthe reference voltages is not as important, although noise andshort-term stability may still be important.

FIG. 6B illustrates the concept of reference voltage calibration processwhen measuring an input voltage VIN. The reference voltages of the ADCdefine its full-scale input range (refer to case 631). The drift of thereference voltages can cause significant degradation of the conversionaccuracy. If the reference voltages drift either higher or lower thanthe ideal levels defined for these reference values, then the outputvoltage of the voltage divider 600 also drifts with the same amount oferror. For example, if the reference voltages drift higher (as shown incase 632 with non-ideal reference values VR_T′/VR_B′), then the outputvoltage of the voltage divider 600 also drifts higher with the sameamount of error ΔV′. Conversely, if the reference voltages drift lower(as shown in case 634 with non-ideal reference voltages VR_T″/VR_B″)then the output voltage of a voltage divider also drifts with the sameamount of error ΔV″.

The drift error, ΔV′ or ΔV″, can be determined by subtracting from ann-bit reference code 620 in the digital domain. The correction processcan be performed in either the analog or digital domain. In an analogcorrection scheme, the magnitude of a drift error is interpreted tochange of the resistance ratio of a voltage divider 600, either bychanging the resistance or the current in a voltage divider. After thecompletion of this part of the calibration process, the battery inputcan be read with an accurately calibrated value (refer to case 633 or635). Thereafter, the correction of reference voltages, VR_T and VR_B,is performed by adding or subtracting the same amount of the errorvoltage, ΔV′ or ΔV″, at the reference voltage generator 602 to sustain aconstant full-scale range of the ADC.

As noted above, a digital correction scheme can also be used to correctthe drift error. In a digital correction scheme, the amount of drifterror at the output of a voltage divider can be calculated and stored inan offset register. The correction of the reference voltages isperformed to sustain the full-scale range of the ADC and to fix theslope of the ADC transfer function (gain error correction).

To guarantee accurate cell-level current measurement, a new currentmeasurement technique is proposed. The conventional approaches employedfor measuring the battery pack current involve using Hall effect sensorsor isolated shunt current sensors at the first or end point of a batterypack connection, as shown in FIG. 1. The Hall-effect sensor technologyis popular and accurate, but is bulky and has relatively high cost.Accordingly, such technology is not considered well suited for currentsensing at the level of an individual battery cell. Moreover, existingshunt resistance current measurement techniques involve the use of shuntresistor components placed in series with each battery cell. Theaddition of such resistance in the current path increases overallresistance of the battery cell, and therefore reduces efficiency. Theadverse effects upon efficiency become particularly problematic inbattery packs containing large numbers of battery cells because each ofthe shunt resistors generate heat and waste energy. The presentinvention overcomes these problems associated with conventional shuntcurrent sensors by using the inherent resistant of the conductive outputterminals of the battery cell as the shunt resistor. With such anapproach, no extraneous resistance is added to the circuit, but a highdegree of measurement accuracy is required since the resistanceassociated with the conductive output terminal is very small, usually onthe order of about 20 micro-ohms.

Referring now to FIG. 7, there is shown a conceptual block diagram thatis useful for understanding the cell-level current measurement. Forconvenience, there is shown an exemplary battery cell 302, which is oneof k battery cells comprising battery pack 306. For purposes of clarity,only a single battery cell 302 of the battery pack and its associatedSCSM 400 are shown. However, it should be understood that the eachbattery cell 302 in a battery pack 306 can be independently measured ina similar manner with its own SCSM.

When the SCSM 400 is used to measure the voltage of a battery cell 302,it requires only a conductive lead BAT_V which allows a voltagemeasurement relative to a reference level or ground potential 706.However, when the SCSM 400 is used to measure battery cell currentI_(CELL, k), of a single battery cell, the SCSM must determine a voltagedrop across a shunt resistance. Accordingly, a second test lead BAT_I isprovided so that the voltage potential across the shunt resistance 708resistor can be measured.

To determine single battery cell current, the SCSM 400 measures avoltage across two conductive pads spaced apart a distance on one of theoutput terminals 702 a, 702 b of the battery cell 302. Although theoutput terminals of the battery cell 302 are formed of a conductivemetal (e.g. aluminum) they will have some inherent level of resistancealong their length. This inherent resistance 708, which is on the orderof micro-ohms, will produce a very small but measurable voltage dropV_(R, k) across the shunt resistance 708 when measured between the twoconductive pads. For convenience, the shunt resistance 708 between thetwo pads is sometimes referred to herein as R_(SHUNT, k). An SCSM 400 isprovided for each battery cell 302 within the battery pack 306 so thatthe voltage V_(R, k) can be measured for each of the k battery cells inthe pack. These values can be stored in a data memory 714, which issometimes referred to herein as Register-V.

For purposes of the present invention, an accurate current measurementmainly depends on the accuracy of determining the shunt resistance andthe uniformity of such determination over different battery cells 302.Accordingly, the process described herein mainly involves a process foraccurately determining a shunt resistance R_(SHUNT, k) of each batterycell.

After a battery pack 306 is assembled, an initial pack current(I_(PACK)) is precisely measured by using the current sensing device704. In FIG. 7, the master module 310 receives data concerning the totalinitial pack current I_(PACK) for battery pack 306 from a currentsensing device 704, which may be a Hall-effect sensor. The data receivedat the master module 310 is stored in a suitable memory device 710,which is sometimes referred to herein as Register-I. Concurrently, anSCSM for each battery cell 302 measures the voltage across the shuntresistor (V_(R,k)). This voltage value is communicated to the mastermodule 310 as shown. Thereafter, the effective shunt resistanceR_(SHUNT,k) of each battery cell 302 is extracted by dividing V_(R,k)for each cell by the measured value of I_(PACK)/P (where P is the numberof cells connected in parallel within each module. In such a scenario,I_(PACK)/P represents the theoretical value of current flow through eachbattery cell in a module 304, assuming that each battery cell (at leastwhen first assembled as part of the battery pack) passes the same amountof current.

Once the value of R_(SHUNT,k) has been determined for each battery cell302, it is stored in a digital data memory device 712, which issometimes referred to herein as Register-R. At this point the mastermodule 310 can begin monitoring the cell current of each individualbattery cell 302 as the battery pack is used. In particular, once theR_(SHUNT,k) for all the battery cells 302 are extracted, the respectivevalues are utilized to derive the I_(CELL,k) (t) for each of the batterycells. This is accomplished by dividing V_(R,k) (t) by R_(SHUNT,k),where the I_(CELL,k) (t) and V_(R,k) (t) are values which areperiodically obtained over time once the battery pack has been put intoservice. Over the life of the battery pack, the value of I_(CELL,k) (t)can be monitored by the master module 310 to determine if the valuefalls outside of certain predetermined limits. The master module canalso generate a suitable notification (e.g. a notification to a user) ifone or more battery cells are determined to have values that falloutside the predetermined limits. In some scenarios, such notificationcan include a specific battery cell that is determined to beexperiencing current values falling outside predetermined limits.

FIG. 8 illustrates an exemplary architecture of a sensing circuit 800which can be integrated in each SCSM 400 for purposes of facilitatingcurrent sensing. The sensing circuit 800 includes two voltage dividers802 a, 802 b which are connected to the conductive leads for BAT_V andBAT_I as described with reference to FIG. 7. In some embodiments,voltage divider 600 can be used for voltage divider 802 a. The sensingcircuit 800 also includes a pair of auto-zeroed (AZ), programmable-gaininstrument amplifiers 804 a, 804 b and a differential amplifier 806. Thevoltage across the shunt resistor 708 (R_(SHUNT,k)) is delivered to thevoltage dividers 802 a, 802 b and processed to be within a suitablevoltage range. The two voltage dividers are selectively calibrated withregard to their voltage division ratios based on the calibrationalgorithm described with respect to FIGS. 6A and 6B. Upper and lowercontrol signals are provided under the control of the calibration engine412 to select the voltage division ratios. The upper and lower controlsignals can be provided from the DACs 618 a, 618 b for each of thevoltage dividers. The instrument amplifiers 804 a, 804 b linearlyamplify the voltage across the shunt resistor 708 with programmable gainsettings. The gain can be adjusted by a gain resistance (RG), based oninformation concerning battery capacity or shunt resistance value. Suchgain adjustments can be performed under the supervision of the controlunit 406 or other gain control circuitry. The common-mode rejection(CMR) and bandwidth of the amplifier are designed to have reasonableperformance. Auto-zeroed amplifiers 804 a, 804 b are well known in theart and therefore will not be described here in detail. However, it willbe appreciated that such amplifiers offer the benefit of low offsetvoltage and offset voltage drift. The outputs of the auto-zeroedamplifiers are connected to the differential inputs of differentialamplifier 806. The output of the differential amplifier 806 is coupledto the S2D which provides the sensed analog voltage to n-bit ADC 410.The ADC provides the output data to a suitable data transceiver so thatit can be communicated to a master module 310.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

We claim:
 1. A sensing system for a battery pack which includes amultiplicity of battery cells, comprising: a multiplicity of single cellsensing modules (SCSM), each SCSM respectively configured to facilitateboth a current measurement and a voltage measurement exclusively withrespect to one of the multiplicity of battery cells in the battery pack;each SCSM comprising an analog switching multiplex; an analog-to-digitalconverter (ADC); a signal conditioner which conditions an input signalreceived at the analog switching multiplex and communicates the inputsignal after conditioning to the ADC; a reference voltage generatorwhich generates a plurality of reference voltages; and a calibrationengine which is configured to use the plurality reference voltages toimprove a measurement accuracy with respect to the input signal; whereineach SCSM is configured to facilitate the current measurement of aparticular battery cell by determining a voltage drop between first andsecond locations spaced apart a predetermined distance along an outputterminal of the battery cell.
 2. The sensing system according to claim1, wherein the calibration engine is configured to determine a drifterror.
 3. The sensing system according to claim 2, wherein the referencevoltage generator generates top and bottom reference voltages whichdefine the full-scale input range for the ADC.
 4. The sensing systemaccording to claim 3, wherein the top and bottom reference voltages areapplied to inputs of the signal conditioner in a calibration conditionto generate an output calibration voltage, and the calibration engine isconfigured to determine the drift error value by calculating adifference between a predetermined reference value and a measured valueoutput of the ADC in the calibration condition.
 5. The sensing systemaccording to claim 4, wherein the signal conditioner includes a voltagedivider and the calibration engine is configured to automatically usethe drift error value to adjust the voltage divider.
 6. The sensingsystem according to claim 5, wherein the calibration engine isconfigured to automatically adjust the top reference voltage and thebottom reference voltage based on the drift error value which has beendetermined.
 7. The sensing system according to claim 1, wherein theanalog switching multiplex is configured to select when in a sensingmode one or more of a plurality of the input signals from the particularbattery cell and wherein the input signals is selected from the groupconsisting of a voltage sense signal and a current sense signal.
 8. Thesensing system according to claim 7, wherein the analog switchingmultiplex is further configured to select as the input signal atemperature sensor signal associated with the particular battery cell.9. The sensing system according to claim 1, wherein the SCSM isconfigured to measure the voltage drop as caused by an inherentresistance of a portion of the output terminal.
 10. The sensing systemaccording to claim 9, wherein the signal conditioner includes twovoltage conditioners which respectively independently condition an inputvoltage potential at each of the first and second locations.
 11. Thesensing system according to claim 10, further comprising a mastercontroller which receives from each of the SCSM a value which specifiesthe voltage drop for each of the battery cells.
 12. The sensing systemaccording to claim 11, wherein the master controller is configured tocalculate a shunt resistance value associated with each single batterycell using the value which specifies the voltage for each battery celland based on a total battery pack current measured at a time when thebattery pack is first assembled.
 13. The sensing system according toclaim 12, wherein the master controller is configured to determine anindividual battery cell current for each of the battery cells by usingthe shunt resistance value and the voltage drop for each battery cell asmeasured at each of the SCSM.
 14. The sensing system according to claim13, wherein the master controller automatically determines a conditionof each battery cell based on the battery cell current for each battery.15. The sensing system according to claim 12, wherein the total batterypack current is determined using a Hall-effect sensor at a battery packoutput terminal.
 16. A sensing system for a battery pack which includesa multiplicity of battery cells, comprising: a multiplicity of singlecell sensing modules (SCSM), each SCSM respectively configured tofacilitate both a current measurement and a voltage measurementexclusively with respect to one of the multiplicity of battery cells inthe battery pack; each SCSM comprising a calibration engine configuredto reduce measurement errors; and wherein each SCSM is configured tofacilitate the current measurement of a particular battery cell bydetermining a voltage drop between first and second locations spacedapart a predetermined distance along an output terminal of the batterycell.
 17. A method for determining battery cell current and battery cellvoltage for a multiplicity of battery cells associated with a batterypack, comprising: providing a multiplicity of single cell sensingmodules (SCSM) respectively for monitoring a multiplicity of batterycells in the battery pack; exclusively using each of the multiplicity ofSCSM to respectively facilitate both a current measurement and a voltagemeasurement for a corresponding one the multiplicity of battery cells;for each of the battery cells, facilitating the current measurement byprecisely determining a voltage drop between first and second locationsspaced apart a predetermined distance along an output terminal of thebattery cell.
 18. The method according to claim 17, further comprisingperforming at least one calibration operation to facilitate the precisedetermination of the voltage drop.
 19. The method according to claim 17,further comprising determining for each battery cell a resistance valueassociated with the electrical path between the first and secondlocations.
 20. The method according to claim 19, further comprisingdetermining the resistance value for each cell at a time when thebattery pack is first assembled.
 21. The method according to claim 19,further comprising using the resistance value which has been determinedfor each battery cell, and the voltage drop which is measured during abattery management session, to calculate the battery cell current.
 22. Asensing system for a battery pack which includes a multiplicity ofbattery cells, comprising: a multiplicity of single cell sensing modules(SCSM) respectively provided for the multiplicity of battery cells, eachSCSM in communication with a master control module; each SCSMrespectively configured to facilitate both a voltage measurement and acurrent measurement exclusively with respect to one battery cell of themultiplicity of battery cells in the battery pack; and a datatransceiver to facilitate communications with the master control module;wherein each SCSM is configured to facilitate the current measurement ofa particular battery cell by determining a voltage drop between firstand second locations spaced apart a predetermined distance along anoutput terminal of the battery cell.